Conflicting VLANs on Catalyst switch

[reinderien]

I have a very old switch, a WS-C2950C-24. I've tried IOS both C2950-I6K2L2Q4-M, Version 12.1(22)EA7 (what I got it with) and EA14 (the most recent one I could dig up on the fora, since Cisco no longer offers this download). I've tried flashing via xmodem and tftp.

The switch exhibits a very strange behaviour. I have FastEthernet 0/24 configured as a trunk for VLANs 2,4, the other ports configured as access to VLAN 4, and the only interface with an IP address assigned is VLAN2.

If I try to noshut the interface for VLAN4, VLAN2 is shut, and vice versa. Even more strangely, when I attempt to noshut the interface for VLAN4, it steals the IP that I put on VLAN2, and VLAN2 loses its IP.

What's going on here?

[Julio E. Moisa · Accepted solution]

Hi

Please check this link:

https://supportforums.cisco.com/t5/lan-switching-and-routing/cat-2950-3-vlans-one-keeps-shutting-down-when-i-activate-the/td-p/1861523

Apparently this model does not allow IP addressing for 2 or more SVI.  You can have just a SVI and destined for management only. It is a different behavior than other models like 2960+

Hope it is useful

:-)

[reinderien]

OK. So, to be clear - if I create an interface for a VLAN, if it's shutdown it will still be switched; and if it's no-shutdown then it's implied that it should have an IP? I might as well delete the interface entirely, if the VLAN can still be switched without it.

[Julio E. Moisa]

Hi

Actually you need a SVI to manage the device remotely otherwise you will be able to manage the switch via Console only. You must keep 1 SVI on that specific model. On other models you can have multiple SVI with IP address but just one will be used for management and that SVI will be associated to the default-gateway command. 

[paul driver]

Hello

---

@Julio E. Moisa wrote:

Hi

Actually you need a SVI to manage the device remotely otherwise you will be able to manage the switch via Console only. You must keep 1 SVI on that specific model. On other models you can have multiple SVI with IP address but just one will be used for management and that SVI will be associated to the default-gateway command. 

Hmm.. not necessarily true Julio - Totally agree to remotely admin a single switch a SVI is required- However for switches that are physically attached to say distribution switche or other switch’s that need an SVI then the ones that don’t need an SVI can still be accessed remotely via switch clustering..

Clustering is reliant on it neighbouring switch ( say a distribution switch) to have an SVI bit in a large Distribution network where the access switches are physically connected to the dis switch then it could be very useful if the need arises that you’ve lost connection to a l2 switch and need to remote access to it.

I use it mostly when adding new switches to exisitng stacks, I just get the local guy to physically attach the switch to a switchport on the stack and then I jump on to it, pre-configured it and then get them to physcally attach it correctly after this...works a treat!

res
Paul

[Julio E. Moisa]

Hi

I agree, but I was pointing to access switches only i think that was missed hehe. We could jump from one switch to other without configuring ip default-gateway command but I prefer include it to avoid that. 

[reinderien]

Right; I understood that much; I was talking about VLAN 4 that does not need an IP but still needs to be switched. Put another way, is there any point in having an "SVI"that does not have an IP?

[Julio E. Moisa]

Hi

Actually there is no reason to have an empty SVI. 

[paul driver]

Hello

Yesi I agree with Julio - some of the older switches are just pure Layer 2 and as such only allow 1 svi for mgt purposes.

res

Paul